Think a cog is just a circle with spikes? Think again! Cogs have been used to map the stars, travel along the Great Wall, and even race in the Tour de France. This Mighty Models title highlights ten important key moments in which the cog leveled up in history--from being a wheel to a telescope in space. Readers can build their own working pendulum clock, using the build-it-yourself model included in the book, to see the power of the cog in action! Christine Van Zandt's nonfiction STEM series for readers 4 to 8 and up perfectly captures the marvels of early machinery and how it plays into today's technology.